Westerlund 2 is an obscured compact young star cluster (perhaps even a super star cluster) in the Milky Way, with an estimated age of about one or two million years. It contains some of the hottest, brightest, and most massive stars known. The cluster resides inside a stellar breeding ground known as Gum 29, located 20,000 light-years away in the constellation Carina.
The cluster contains a dozen O stars, of which at least three are eclipsing binaries, many pre–main sequence stars and two Wolf–Rayet stars: the binary WR20a and the single star WR20b, all of spectral type WN6ha. They are probably not actually Wolf-Rayet stars, i.e. they are core-hydrogen-burning stars, just like the sun, but due to their large mass loss rate they appear to be Wolf Rayet stars.
It was shown recently that the core of the cluster contains several examples of rare very hot stars. Just outside the cluster a massive eclipsing binary WR20a is found at 30 arcseconds (about 1.1 pc in projection), the bright yellow spot just on the lower right side of the cluster center.
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- Rauw et al. (1 March 2007). "Early-type stars in the core of the young open cluster Westerlund 2". Astronomy & Astrophysics 463 (3): 981–991. doi:10.1051/0004-6361:20066495.
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